From the moment he first met her behind a potted plant in 1975, Alan Zweibel loved Gilda Radner. Despite the unwieldy and inaccurate subtitle, “A Sort of Love Story,” the play “Bunny Bunny,” now at the Mercury Theater in Chicago, makes that very clear.

The two never married, of course. Radner, who was one of the seven original cast members of “Saturday Night Live,” first married show guitarist G.E. Smith and then the movie star Gene Wilder. The comedy writer Zweibel, who wrote with Radner and penned most of the words behind her recurring characters like Emily Litella, Baba Wawa, Roseanne Roseannadanna and Candy Slice, eventually married Robin Blankman, a production assistant at “SNL.”

Yes, this was the era when people met at work and relationships were a blur of the personal and the professional, which God knows is the truth about Radner and Zweibel, even if their deeply complicated relationship remained physically platonic. (Her choice, it feels, not his.) She called him Zweibel, he called her Gilbert, to separate her from the fans who would yell “Gilda” every time she walked down the street. “Bunny, Bunny” thus now plays very much as a period comedy — it’s soft-focused, of course, and inherently emotional, given that Radner died of ovarian cancer in 1989, when she was just 42 years old.

I’d seen “Bunny Bunny” before, years ago. It was written in 1994 as a memoir of a 20-year relationship, penned in dialogic form only because its subjects were a joke writer and a performer. It felt like the kind of thing writers do for therapy when someone they love dies. You get to see small snippets of the famous Radner/Zweibel routines, such as the hilarious “Let’s Talk Dirty to the Animals,” which Radner performed in her 1979 Broadway show. But Zweibel had to be careful with rights clearances, I suspect. And “Bunny, Bunny” did not feel like much of a play.

Last Friday night on Southport Avenue, I revised that view.

The main reason was Dana Tretta, who plays Radner in director Warner Crocker’s very funny little production at the Mercury Theater. Tretta has done plenty of shows in Chicago, but they’ve almost all been musicals and I’d not seen her doing anything quite like this. Plus I feel uneasy about anyone assuming the Radner persona, given Radner’s connection to Second City, the importance of Gilda’s Club and any number of other historical reasons, not the least of which was the Gilda history, rather variant from this play, that I’d heard from the late Joyce Sloane at Second City; no one loved Radner more than Sloane.

But Tretta’s performance is really one to see: she captures the essence of Radner by homing in on her vulnerability and emotional openness, not her wacky bombast. Yet this is also a very assertive performance that keeps reminding you of a truth: Radner was one of the funniest, and most influential, women in the history of American comedy.

Zweibel was an emotional bit of jelly, too, and Jackson Evans makes him very likable in the nebbish kind of way. If you were writing this piece now, you’d make it a one-act. But I sat with a very small audience at Friday night’s preview and, after some palpable initial resistance, we all chuckled together as if the spirit of Gilda were in the room.

Zweibel’s main device in “Bunny Bunny,” which his own persona narrates, is to use one actor to play any number of small roles, from Andy Warhol to Richard Carlton to a FedEx dude. Crocker has the Second City alum Jason Grimm in that job, and he’s dry like sandpaper.

The passage of time has been good to this show, which also has re-emerged of late in Los Angeles. It has the aura now of midcentury modern, retro, comedy-club chic. Our collective obsession with “Saturday Night Live” has kept on going. This isn’t one of those authorized exhibitions, of course, but a very personal little love story, about those friendships that some of us have that never quite tip into eros, even if we come to wish they had. Especially after our soul mates no longer walk this earth and make us laugh.

It’s safe to go if you are a Gilda devotee — desirable, even. You’ll like Tretta in this part of parts.